The invention relates to a hydrostatic support member for supporting a surface which is slidably mounted relative to the support member, via a film of fluid located between a head portion of the support member facing the surface and the surface itself, wherein for creating pressure in the film of fluid the head portion comprises at least one pressure pocket which opens opposite the surface and is defined relative to the environment of the support member by a lining wall, the or each pressure pocket being supplied with a pressure fluid by a feed line passing through the support member from a pressure chamber which is provided in a stationary carrier in order to actuate the support member and which is acted upon by the pressure fluid.
Support members of this kind are known, for example, from U.S. Pat. No. 3,802,044, in which case they are used for supporting a roller shell mounted so as to be rotatable about a carrier. The support member is embedded in the carrier like a piston acting relative to the pressure chamber and is forced towards the inner surface of the roller shell with a force corresponding to a function of the pressure in the pressure chamber and the hydrostatically effective surface of the support member opposite the pressure chamber. However, the pressure fluid then flows out of the pressure chamber, through the feed line and into the pressure pocket, where a pressure builds up which, as a function of a correspondingly large hydrostatically effective surface of the head portion, produces a force which is capable of pushing the head portion away from the roller shell, with the result that a gap is formed between the inner wall of the roller shell and the lining wall which defines the pressure pocket relative to the environment of the support member, through which gap the pressure fluid flows away into the surrounding area, i.e. into the space between the inner wall of the roller shell and the carrier. During this passage of the pressure fluid, there is a drop in pressure, from the pressure of the pressure fluid fed in the pressure pocket and the atmospheric pressure at the outer edge of the lining wall defining the pressure pocket. A film of fluid is formed between the head portion and the inner wall of the roller shell, the thickness of this film corresponding to the clearance between the inner wall of the roller shell and the wall which defines the pressure pocket.
It is known that, in order to form a film of fluid capable of bearing a load, there must be hydrostatic equilibrium between the hydrostatically effective surface of the head portion and the hydrostatically effective surface of the support member opposite the pressure chamber. Otherwise, there would be metal friction between the roller shell and the head portion. However, if there is an unbalance with regard to the head portion, i.e. if the hydrostatically effective surface of the head portion is too large, an excessively large gap is formed between the parts, resulting in too great a throughflow, i.e. too great a consumption of the pressure fluid. This consumption then becomes unacceptable, particularly when high pressures are used. It is evident that minimum consumption of pressure fluid is desirable. It is possible to calculate the optimum hydrostatically effective surface of the head portion in order to minimise the pressure fluid consumption. To do so, not only the surface of the opening of the pressure pocket, but also the width of the lining wall at the gap in the radial direction with respect to the pressure axis of the support member have to be calculated. However, in the production of the head portion, as regards the hydrostatically effective surface, one is limited by the technilogical production limits, as the tolerances to be adhered to are very narrow. Consequently, the degree of reproducibility is also poor.